Aeration and curing apparatus, particularly for rubber dispersions



Sept. 21, 1954 ou m, JR 2,689,374

AERATION AND CURING APPARATUS, PARTICULARLY FOR RUBBER DISPERSIONS FiledMay 25, 1950 2 Sheets-Sheet 1 MIX l 2 GAS RELEASE l FOAM lk/ls ABOUT500% AVULCANIZE IN FOAMED CONDITION mvsmoa HARRY A. TOULMIN JR.

U oubnim Z ATTORN E YS Sept. 21, 1954 H. A. TOULMIN, JR 2,689,374

AERATION AND CURING APPARATUS, PARTICULARLY FOR RUBBER DISPERSIONS FiledMay 25, 1950 2 Sheets-Sheet 2 INVENTOR HARRY A. TOULMIM JR. av

{um I ATTORNEYS Patented Sept. 21, 1954 hair so STATES. PATIENT OFFICE:AEBATJON AND CURING APPARATUS, PAR- 'TICULARLY .FOR RUBBER 'DISPERSIONS1 This invention relates to apparatus useful in the production of spongerubber; more particularly the invention relates to apparatus useful "inthe stirring and *aerationof rubber dispersions.

This'application isadivi-s'ion of my-co-pending application, Serial -No.116,537,'nled September I9, 1949, now Patent No. 2,576,318, :datedNovember 27, i951, and assigned "to "the same assignee as the presentinvention.

In the past, foam rubber products have been prepared byincorporatingsuitable-gas into a rubber dispersion and vulcanizing *thefoam products in molds. Thenature of such procedures and the apparatusemployed malre batchwise operations anecessity.

This prior art process is=u high lmit cost operation because or thenumber -'of expensive molds which are :necessary and the Elength 'oftime each moldtmust be tied mp Ito womanizer-any appreciable thicknessofioam product.

F113 :is an rob iect :of the present invention to provide apparatus"which assists overcoming the disadvantages and limitations of theprocesses knownsheretoiore.

It :is :another robject of ii-he present invention to provide zapparatusiuseiul the continuous aeration and dormingrof shaped-objects.

It is a 'still fimither .nbiedt .of fithis invention to provideapparatus incapable of aerating @and Leontinuously discharging :a:ruhber idispersion froma tankimsfoamingcconditiocn.

It is a further object of the present'inventiontoprovideimexpensivemppananis ifOi continuously aerating,shapingacuringrand:cuttingispong mum ber. r V l i I it. is:amotheriobjedtiof this invention to aproviideinexpensive-apparatusiiorsforniing sponge' rubber objects such asgaskets and the like.

In brief, the apparatus 'ofinvention comprises auger mixingequipmentincluding-,aa nonsmher or tankihavingzaihollowshaft iaxiall yrmounts edtherein which shaft is provided with a helical vane. Longitudinallyspaced ports open to the :5 TGlaims. (Cl. 18-12) chamber from thekhollowshaft betweri the flights of the wane, and in'the process of utilizingthe equipmentwrubber dispersion*is continuously passed through thepo'rtsandinixed with aerat ing gases in the chamber; ithis aerated product iscontinuously discharged =irom""the chamber to a coagulation and curingzone undcr thein'fluence oftl re auger type adtion-oi the apparatus.

1 from 0*seconds"t0 30 minutes. "Ingeneral, for H the purposes oflthisinvention, it is preferred .that

This auger type mixer not only mixestiiegas,

and dispersion, but also "directs the aeratedmixture to the point whereit is dischargedto a coagulation zone. Theistahle foam iormed is Nilcanized in this condition .to .a spon y C lular mass.

In this process natural as well as synthetic rubbers or their :mixturesPare-applicable. Thus, the term dispersion :is 10 the .mrderstood tsmean any dispersion of a rubber and rubber-like substance, includingsynthetic, reclaim partially prevulcanized and natural rubbers inacolloidal suspension form.

Neoprene, butadiene polymers, as "for example, butadiene-styrene,butadiene-acrylonitrile polymers, polyvinyl chloride, and otherequivalent latices *have'been found especiallysatisfactory.

It is essential to the instant invention thatthe foams quickly attainstability in order that they maybe cured while standing in air.

"One method of obtaining stability in the foams is the use of a-delayedaction coagulant. These delayed. action =coagulants or gelling agentsare, for "example, polyvinyl methyl ether, sodium silico fluoride,ammonium sulfate, and equivalent salts of weak bases and strong acids.

The dispersions may be compounded with stabilizers, the abovementionedgelling agents, activators or accelerators, latex thickeners,and the of densities, ranging from 0.1, whiohis a highly expandedfoam/to .8 or 9, which is a relatively dense foam'; j i

It-will "atonce' be recognized that the rubbery material surroundingeach" gas pocketwill be in a highly attentuated 'stateand' imparts.soft1yieldlug-characteristics.

A gelling'agentsuch as sodium si1ico fluoride is added tothese rubberdispersions .in, quantities,

ranging from 51130 5% by Weight of the dry solids "in' the dispersion,with the preferred amount bens pu 1=%. a

Y djustment of the pH ation may be causedto occur over a period .of

theexpanded foams gel in a period ranging from '3 to 'lniinutes.

Whenit is preferred that the dispersions be at a 1515 approximatelyneutral at the time of foaming, stabilizers may be added to preventcoagula- 'parts of dispersion to-5 parts per parts of disof thedispersion, gelpersion. The amount is determined not only by the pH ofthe latex composition, but also the type of solids content, gellingagent, and like variables. Other useful stabilizers which may beutilized in quantities ranging from 0.2 to 2 parts per 100 parts ofdispersion are ammonium caseinate and potassium castor oil soap.

Inasmuch as the foams are to be vulcanized, numerous agents may beintimately mixed into the dispersion, preferably activators oraccelerators for the curing operation, such as zinc diethyl dithiocarbamate, zinc salt of 2 mercaptobenzothiazole, and equivalentpolyvalent metal products.

Another agent in common use is zinc oxide. Zinc oxide is a mild gellingagent when used in conjunction with an acid gelling agent as well as acuring activator.

The action of the above described reagents is in no way hampered byaddition of foam stability agents, as for example, the soaps.

Latex thickeners may also be employed for increasin the foam stability.An example of a latex thickener is a solution of methyl cellulose.

The temperature of vulcanization depends upon the type of rubber, itsaccelerators, and so forth. Th time for vulcanization likewise varies.

The problem involved in its solution is well known in the rubberindustry and. needs no description here, except that an oven temperatureof from 200 to 250 F. has been found satisfactory.

The length of time fOr heat treatment varies greatly depending upon suchfactors as thickness of the foam and the like.

The invention will be more fully understood from the followingdescription taken in connection with the accompanying drawings in which:

Figure 1 is a fiow sheet; and

Figure 2 shows an apparatus embodyin the invention in elevational viewWith the front mixing chamber wall cut away to show the auger type mixerand with a heating coil in position.

Figure 3 is a view in slightly enlarged section taken as on line 3-3 ofFigure 2 with the heating coil removed; and

Figure 4 is an enlarged sectional view taken as on line 44 of Figure 2and clearly illustrating a formed gasket.

Referring to Figure 1 there is represented a mixing station I0.Compounded rubber dispersion prepared at this station moves to theaeration station through l2.

Aeration station II is a closed chamber within which is rotated an augertype mixer 20. Auger 20 consists of a shaft 2| driven from a source ofpower, not shown, upon which are mounted transverse arm units 22 whichmay consist of flights, helical vanes, and the like, of reducing radiusas the outlet or release zone I3 is approached.

Gas is fed to station I through-conduit l4 and is stirred into a rubberdispersion therein.

Released aerated rubber dispersion moves to a foaming or expansionstation I 5 through conduit l5. From the foaming station. l5, the stablefoam expanded to about 500% in volume (a density of about 0.1) isconducted by suitable means indicated at H, which may take the form of abelt or conduit or equivalent means, to a vulcanizing station l8 wherethe foam is-cured to a permanent sponge.

Referring to Figure 2 for an adaptation of the invention whereinapparatus is illustrated for the continuous production of sponge rubbergaskets,

. 4 the apparatus consists of a hopper 30 through which a compoundedrubber dispersion is moved to an aerating chamber 3 I.

Chamber 3| is provided with a mixer unit 32. Mixer unit 32 is composedof a horizontally disposed shaft 33 having a transversely disposedhelical vane 34 of continuously reducing radius mounted thereon. Shaft33 is mounted for rotation and adapted to be driven by a source of poweras motor 39 and belt 46 operable over pulleys 41, 49. Shaft 33 is hollowand provided with ports 35. An outlet conduit 36 of hopper 30 isconnected to said shaft 33 through a suitable rotary seal 50.

Agas inlet 31 is also connected with a conduit 38 for introduction ofgas into the chamber 3|.

In axial alignment with the shaft 33 there is provided an outlet forchamber 3|. This outlet for the chamber 3| is provided with a connectingfrustro-conical conduit 40. Axially mounted within conduit 40 (Figure 3)is a tubular rod 4| defining the shape of an annular chamber 42.

Conduit 40 terminates in a trough section 43 to which the product suchas gasket 48, shown more clearly in Figure 4, is passed in the operationof the apparatus. section 43 are adapted (Figures 2 and 4) with suitableheating means 44, such as helical steam heating coils, radiant heaters,or the like.

Adjacent the terminus of the trough section 43 there is positionedsuitable segmenting means 45, such as, for example, a high speed saw.

Operation of the gasket making equipment is as follows: A compoundedrubber dispersion is flowed into hopper 30. The dispersion flows throughconduit 36 and the shaft 33, and issues into the interior of the chamber3| through ports 35.

ber dispersion with air entering through conduit 38. The helix 34 drivesthe aerated dispersion into the conduit 40 where it is pushed alongcontinuously as an annular shaped rubber tube.

As it passes through the conduit 40 the rubber is cured by subjecting itinitially to heat of about 200 F., followed by final curing at atemperature of about 250 F.

The cured sponge rubber tube supported in trough section 43 of conduit40 is cut into circular gaskets of suitable thickness.

Thefollowing are two illustrative formulation which may be utilized toform gaskets: I

Example I A master mix maybe compounded in the following proportionsfrom an aqueous dispersion of natural latex:

2.8 parts 55% zinc salt of mercaptobenzothiazole dispersion With themixture at room temperature, the following ingredients may be added withgood agi-m tation in the order and quantities specified:

9.0 parts 50% zinc oxide dispersion 6.0 parts 40% Fleischmans yeastsolution Conduit 40 and its trough The helical stirrer thoroughly mixesthe rub-.

12.0 parts 25% sodium silico fluoride solution 15.0 parts 130 volumehydrogen peroxide solution From each approximately 300 parts ofsoiution-dispersion, approximately 1700 cc. of foam may be obtained.

Example II A dispersion of a synthetic rubber latex, namely,butadiene-styrene polymer, having aproximately 60% total solids, may beutilized as for the mixing of Example I, and mixed into a heat sensitivelatex dispersion by compounding as follows:

230 parts butadiene-styrene polymer GRS 7 4 parts polyvinyl methyl ether8 parts ammonia oleate emulsion 5 parts sulfuric acid 8 parts 35%solution potassium castor oil soap 5 parts zinc oxide 10 parts clay 3parts sulfur 12 parts sodium silico fluoride 1 parts zinc salt of 2mercaptobenzothiazole 55% dispersion When the mixture is at atemperature of approximately 55 F., nitrous oxide gas under a pressuremay be introduced.

This mixture will produce approximately 900 cc. of foam for each 200grams of dispersion, which is stable and does not lose appreciablevolume while being cured.

Conditions in the equipment may be as follows:

Flow rate of dispersion 1 lb. min. Pressure of gas 200 lbs. per sq. in.Temperature of initial vulcanizing 180 to 225 F. Temperature of finalvulcanizing 225 to 280 F. Speed of rotation of helical mixer 2200 R. P.M.

the combination comprising a tank having a wall,

a hollow rotatable shaft axially mounted in said tank, said shaft havingone end thereof mounted in said wall of said tank and the other endthereof closed and terminating within said tank, transverse bladesmounted on said shaft, said shaft having longitudinally spaced portstherein opening between said blades, a fluid inlet conduit connectedwith said hollow shaft at the end thereof mounted in said wall, agaseous inlet for. said tank spaced from said shaft, and a fluid outletfrom said tank in axial alignment with said shaft.

2. In apparatus for stirring and aerating fluids the combinationcomprising a tank having a wall, a hollow rotatable shaft axiallymounted in said tank, said shaft having one end thereof mounted in saidwall of said tank and the other end thereof closed and terminatingwithin said tank, a helical vane mounted on said shaft, said shafthaving longitudinally spaced ports therein opening between flights ofsaid helical vane, a fluid inlet conduit connected with said hollowshaft at the end thereof mounted in said wall, a gaseous inlet for saidtank spaced from said shaft, and a fluid outlet from said tank in axialalignment with said shaft.

3. In apparatus for stirring and aerating rubber dispersions thecombination comprising a tank constricting to an axial outlet, said tankhaving a wall, a hollow rotatable shaft axially mounted in said tank,said shaft having one end thereof mounted in said wall of said tank andthe other end thereof closed and terminating within said tank, a helicalvane mounted on said shaft of progressively reducing radius, said shafthaving longitudinally spaced ports therein opening between flights ofsaid helical vane, a fluid inlet conduit connected with said hollowshaft at the end thereof mounted in said wall, a gaseous inlet for saidtank spaced from said shaft, and a fluid outlet from said tank in axialalignment with said shaft.

4. In. apparatus for continuously producing rubber products thecombination comprising a feed hopper for fluids, a closed tank having awall, a hollow rotatable shaft axially mounted in said tank, said shafthaving one end thereof mounted in said wall of said tank and the otherend thereof closed and terminating within said tank, a feed conduitconnecting said hopper and said hollow shaft at the end of said shaftmounted in said wall, transverse blades mounted on said shaft, saidshaft having longitudinally spaced ports therein opening betweensaidblades, a gaseous inlet for said tank spaced from said shaft, afluid outlet in axial alignment with said shaft, an outlet conduit, andheating means surrounding said conduit.

5. In apparatus for continuously producing rubber products thecombination comprising a feed hopper for fluids, a closed tank having awall, a hollow rotatable shaft axially mounted in said tank, said shafthaving one end thereof mounted in said wall of said tank and the otherend thereof closed and terminating within said tank, a feed conduitconnecting said hopper and said hollow shaft at the end of said shaftmounted in said wall, transverse blades mounted on said shaft, saidshaft having longitudinally spaced ports therein opening between said.blades, a gaseous inlet for said tank spaced from said shaft, a fluidoutlet in axial alignment with said shaft, an outlet conduit, heatingmeans surrounding said conduit, and segmenting mean positioned adjacentthe terminus of said conduit.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 548,521 Cummins Oct. 22, 1895 675,163 Overton May 28, 1901824,075 Gerner June 19, 1906 1,166,319 Blichfeldt Dec. 28, 19151,818,372 Battilani Aug. 11, 1931 2,011,160 Plepp Aug. 13, 19352,156,508 Minor May 2, 1939 2,191,450 Campbell Feb. 27, 1940 2,320,469Rasmussen June 1, 1943 2,415,585 Genova Feb. 11, 1947 FOREIGN PATENTSNumber Country Date 618,604 Great Britain Feb. 24, 1949

